This problem only occurs when you have enabled global menus in Ubuntu/Unity.

Technical details:
Quick 'n Easy Web Builder for Linux uses wxWidgets as underlying programming environment.
A bug in Ubuntu/Unity cause problems with dialog windows launched via the global menu bar.
Unfortunately we do not have directly control over this behavior. And suggested 'fixes' do not provide a stable solution at this time.

But there is a simple work around. Run the following command in a Terminal: